1. Technical Field
The present invention relates in general to motor vehicles. More particularly, the present invention relates to a truly unique and versatile assembly of electric motors for a motor vehicle.
2. Discussion
The invention relates to a multi-motor drive which is suitable for motor vehicles and in which two electric motors are assigned to a common output, which can be corrected in terms of drive to driven vehicle wheels, and to an autonomous controller which permits the motors to be operated with different load distribution, the controller permitting a load distribution which brings about an optimum degree of efficiency of the drive to be set automatically as a function of signals of a control element, e.g. accelerator pedal, which can be actuated at the driver""s end, and of a signal transmitter for the travel speed or for a parameter which is correlated to it and/or analogous to it.
Until now batteries have only had a comparatively low energy density so that a battery charge for an electrically driven vehicle can provide a satisfactory range only if the electric drive is capable of operating with a high degree of efficiency. In electric motors the degree of efficiency depends heavily on the respective torque and on the rotational speed. With a multi-motor drive it is now to switch off a motor in travel situations with a relatively low power demand or to make the loading of the motors differ to a greater or a lesser extent in order to achieve a higher average degree of efficiency than would be possible with a drive with just one electric motor.
In a drive of the type specified at the beginning which is known from U.S. Pat. No. 5,289,890, two structurally different electric motors are provided, in such a way that the optimum degree of efficiency of one electric motor lies in the range of relatively low rotational speeds, and the optimum degree of efficiency of the other electric motor lies in the range of relatively high rotational speeds. As long as the power demand for the travel mode is lower than the total of the maximum powers of the two motors, it is possible, depending on the travel speed, to load mainly the one motor or the other motor, i.e. at least one motor operates in a comparatively optimum way.
Accordingly, it is an object of the invention is to permit a further improvement in the degree of efficiency.
This object is achieved according to the invention in that a gearbox which is changed automatically by the controller is arranged in the output, and the controller adjusts in each case to a gearbox state which is optimum with respect to the degree of efficiency.
According to one preferred embodiment of the invention, there is provision to use electric motors of the same type for this.
The invention is based on the general idea of using a change speed gearbox to change the respective motor speed and the motor moment which is necessary for the respective travel state of the vehicle with respect to an optimum degree of efficiency of this. As a result, an increased degree of efficiency is made possible within a significantly enlarged range of operating situations. In particular, it is possible to use two electric motors of the same type to ensure a good degree of efficiency and/or an increased degree of efficiency at both high and low travel speeds, because operating situations with very low degrees of efficiency of the electric motors can virtually always be avoided.
The controller preferably also takes into account the degree of efficiency of the gearbox which is dependent on a wide range of parameters, in particular the rotational speed and torque as well as the temperature, in order to set the load distribution between the motors and to set the respective gear speed with the aim of achieving an optimum overall degree of efficiency of the drive.
For the sake of its robustness and good control characteristics, asynchronous motors are preferred for the invention. Said motors havexe2x80x94expressed in simple termsxe2x80x94generally a good degree of efficiency if, on the one hand, the rotational speed lies above a mean rotational speed value and the motor has to operate with a mean torque. Furthermore, a good degree of efficiency is also achieved if the motor is operating at a mean rotational speed and the respective motor torque lies above a mean value. By appropriately changing the gear speed of the gearbox and connecting into the circuit or disconnecting the second motor and/or by loading the two motors in a non-uniform way it is then possible for the controller to achieve an optimum degree of efficiency.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.